Re: [PATCH v20 3/5] arm64: kdump: reimplement crashkernel=X

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 6c653a2c7cff052..a5d43feac0d7d96 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c

@@ -71,6 +71,30 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
 #define CRASH_ADDR_LOW_MAX	arm64_dma_phys_limit
 #define CRASH_ADDR_HIGH_MAX	MEMBLOCK_ALLOC_ACCESSIBLE
 
+static int __init reserve_crashkernel_low(unsigned long long low_size)
+{
+	unsigned long long low_base;
+
+	/* passed with crashkernel=0,low ? */
+	if (!low_size)
+		return 0;
+
+	low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX);
+	if (!low_base) {
+		pr_err("cannot allocate crashkernel low memory (size:0x%llx).\n", low_size);
+		return -ENOMEM;
+	}
+
+	pr_info("crashkernel low memory reserved: 0x%llx - 0x%llx (%lld MB)\n",
+		low_base, low_base + low_size, low_size >> 20);
+
+	crashk_low_res.start = low_base;
+	crashk_low_res.end   = low_base + low_size - 1;
+	insert_resource(&iomem_resource, &crashk_low_res);
+
+	return 0;
+}
+
 /*
  * reserve_crashkernel() - reserves memory for crash kernel

  *

@@ -81,29 +105,62 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
 static void __init reserve_crashkernel(void)
 {
 	unsigned long long crash_base, crash_size;
+	unsigned long long crash_low_size = SZ_256M;
 	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
 	int ret;
+	bool fixed_base;
+	char *cmdline = boot_command_line;
 
-	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
+	/* crashkernel=X[@offset] */
+	ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
 				&crash_size, &crash_base);
-	/* no crashkernel= or invalid value specified */
-	if (ret || !crash_size)
-		return;
+	if (ret || !crash_size) {
+		unsigned long long low_size;
 
+		/* crashkernel=X,high */
+		ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
+		if (ret || !crash_size)
+			return;
+
+		/* crashkernel=X,low */
+		ret = parse_crashkernel_low(cmdline, 0, &low_size, &crash_base);
+		if (!ret)
+			crash_low_size = low_size;
+
+		crash_max = CRASH_ADDR_HIGH_MAX;
+	}
+
+	fixed_base = !!crash_base;
 	crash_size = PAGE_ALIGN(crash_size);
 
 	/* User specifies base address explicitly. */
 	if (crash_base)
 		crash_max = crash_base + crash_size;
 
+retry:
 	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
 					       crash_base, crash_max);
 	if (!crash_base) {
+		/*
+		 * Attempt to fully allocate low memory failed, fall back
+		 * to high memory, the minimum required low memory will be
+		 * reserved later.
+		 */
+		if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
+			crash_max = CRASH_ADDR_HIGH_MAX;
+			goto retry;
+		}
+
 		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
 			crash_size);
 		return;
 	}
 
+	if (crash_base >= SZ_4G && reserve_crashkernel_low(crash_low_size)) {
+		memblock_phys_free(crash_base, crash_size);
+		return;
+	}
+
 	pr_info("crashkernel reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
 		crash_base, crash_base + crash_size, crash_size >> 20);
 

@@ -112,6 +169,9 @@ static void __init reserve_crashkernel(void)
 	 * map. Inform kmemleak so that it won't try to access it.
 	 */
 	kmemleak_ignore_phys(crash_base);
+	if (crashk_low_res.end)
+		kmemleak_ignore_phys(crashk_low_res.start);
+
 	crashk_res.start = crash_base;
 	crashk_res.end = crash_base + crash_size - 1;
 	insert_resource(&iomem_resource, &crashk_res);

-- 
2.25.1